W124 , !988
I heard a metallic thunk coming from the left rear wheel every time I rolled over a bump except when I was braking at the same time.
The noise was actually made by the whole caliper assembly which was loose. The two bolts holding it to the car were tightened all the way, but there was still some play. I inserted washers and that took care of the play and also of the noise.
Hope this helps.
jacques.